Seismic Assessment and Retrofitting of a Non-Conforming CBF Structure

Concentrically Braced Frames (CBF) represent one of the most common structural typologies adopted for steel buildings. Although new CBF structures can assure excellent seismic performances, existing braced structures were often designed accounting only for wind loads and with poor local detailing. The present paper is focused on local assessment and retrofit of concentrical bracing system of an existing non-conforming steel building. Geometry of investigated CBFs has been determined on the basis of on-site surveys. CBF assemblies have been sub-structured and analyzed against seismic actions. As expected, analyzed bracing systems show a very poor seismic response since local detailing was overlooked in the design process. Therefore, a retrofit intervention (i.e. brace replacement with RHS sections) has been designed and numerically tested. The comparison between existing and retrofitted scenarios is presented to highlight the intervention efficiency in terms of improvement of the seismic performance.